1. Field of the Invention
This invention relates, in general, to electrical inductive apparatus and, more specifically, to vaporization cooled electrical inductive apparatus.
2. Description of the Prior Art
Vaporization cooling systems have been proposed for electrical inductive apparatus, such as transformers, reactors and the like, utilizing a two-phase dielectric fluid which has a boiling point within the normal operating temperature range of the electrical inductive apparatus. The dielectric fluid is applied to the electrical inductive apparatus in its liquid state, whereon it evaporates as it contacts the heat producing members and removes heat in quantities equal to the latent heat of vaporization of the dielectric fluid. The resulting vapors are then condensed and reapplied to the heat producing elements in a continuous cycle. In a typical vaporization cooling system for a transformer, the windings contain a plurality of vertically extending ducts. The dielectric fluid must be distributed uniformly over the vertical ducts to insure even cooling of the windings and thus prevent the formation of hot spots within the transformer. Typical methods of applying the dielectric fluid in uniform quantities through the ducts include the use of spray devices or headers having a plurality of apertures therein which are disposed above the transformer, as shown in U.S. Pat. Nos. 2,561,738 and 2,875,263, and also the use of perforated plates or pans disposed above the transformer as shown in U.S. Pat. Nos. 3,024,298, 3,887,759 and 4,011,535.
In operation, transformers encounter frequent and severe short circuits which generate horizontal and vertical forces on the windings on the order of several hundred thousand pounds. The horizontal forces, which cause the low voltage coil to compress against the core and the high voltage coil to be stressed in tension, are restrained by the use of end frames and lock plates which rigidly brace the coils against the core. The vertical forces, which are caused by radial flux components and the axial displacement of the electrical centerlines of the windings, are restrained by the use of pressure rings which are typically circular plates disposed above the windings and interlocked to the end frames to distribute the vertical forces uniformly from the coils to the end frames to prevent any vertical displacement of the windings.
The use of pressure rings effectively blocks off the ends of the ducts extending through the windings since the pressure ring must be disposed immediately adjacent with the windings to prevent any vertical displacement thereof. In certain electrical inductive apparatus, which utilize oil as the dielectric coolant fluid, baffles or ducts are provided around the pressure ring to provide a fluid flow path for the oil through the windings of the transformer. Such a construction cannot be used in vaporization cooled apparatus since the vaporizable fluid flows through the ducts and the windings from top to bottom which is directly opposite that of an oil-cooled transformer wherein the oil coolant is forced through the ducts and the windings from the bottom to the top of the transformer. Furthermore, the use of baffles around the pressure ring does not provide the uniform distribution of the vaporizable fluid across the surface of the windings which is essential in preventing hot spots from developing in the windings of the transformer.
In multi-phase transformers, a core yoke is used to connect the cores in each phase. In such constructions, the portion of the windings disposed beneath the core yoke are blocked from the direct flow of the dielectric fluid such that a temperature gradient is formed in the windings.
The liquid distribution systems utilized in prior art vaporization cooled electrical inductive apparatus do not provide a uniform distribution of the dielectric fluid to the portion of the windings located beneath the pressure rings or the core yoke since such liquid distribution systems utilize spray devices located above the electrical apparatus.
Thus, it would be desirable to provide an improved fluid distribution system for a vaporization cooled electrical inductive apparatus that uniformly distributes the dielectric fluid over the entire surface of the windings. Further, it would be desirable to provide a fluid distribution system that enables the dielectric fluid to be applied beneath the pressure rings and beneath the core yoke of the electrical inductive apparatus.